1. Field of the Invention
The present invention relates generally to medical treatment apparatus. More specifically, the present invention relates to a ring vortex aerosol projection apparatus for providing medication in a vapor form to the lungs of a patient having asthma or a like medical condition.
2. Description of the Prior Art
Patients suffering from asthma or any of the many other lung diseases require delivery of medication to the bronchi in the lungs. At the present time there are three major ways of delivering aerosol treatment or medication to such patients, namely (1) nebulizers, which may be of the (a) venturi-jet type, or of the (b) ultrasonic piezoelectric type which produce aerosols from drug solutions; (2) metered dose inhalers (MDI) consisting of fluorocarbon or other gas pressurized canisters; and (3) dry powder inhalers (DPI) which may be (a) passive or (b) active. Dry powder inhalers also provide metered doses if sufficient suction is supplied by the patient.
Metered dose inhalers which are both MDI and DPI have certain advantages over nebulizers because they are readily portable, and do not generally require an external power source such as compressed air or electricity. Metered dose inhalers are also capable of generating aerosols that are suitable for inhalation, more efficiently, reliably and cost effectively. The pressurized canister type of aerosol generator (MDI) includes a valve, which, when actuated, causes dispersement of a metered quantity of drug.
Because metered dose inhalers have previously used a chlorofluorocarbon as the propellant, and chlorofluorocarbons are believed to have a highly adverse effect on the ozone layer surrounding the earth, they are gradually being phased out to be replaced by the environmentally more friendly hydrofluorocarbons (e.g., HFC 134a and 227).
Such metered dose inhalers have become popular in that a droplet aerosol consisting of the drug particles and the fluorocarbon propellant is generated. The fluorocarbon propellant evaporates rapidly, and leaves smaller drug particles and clumps of particles, at least some of which are on the order of 1-3 microns aerodynamic mass median diameter which is the ideal size range for medication aerosols in humans. Unfortunately, many of the particles remain in larger clumps, and do not reach the necessary areas in the bronchi and lungs.
For example, some metered dose inhalers are relatively inefficient because they produce mainly non-respirable particles that range in size from about 35 micro-meters to about 1 micrometers. Of these particles only about 30 percent, chiefly particles under 5 micrometers, are actually capable of being inhaled. In practice this figure is closer to 20 percent. Most of the rest of the aerosol which is deposited in the throat has the potential for causing side effects, while not contributing to the therapeutic benefit.
There are some currently available powder inhalation systems which do not require a propellant. However, they do not function very effectively unless the patient can generate flow rates greater than 30-60 liters per minute, since it is the energy provided by the patient's forceful inhalation that not only mobilizes the powder but also breaks up the clumps thus preparing it for inhalation, in contrast with the high pressure of the fluorocarbon or other propellant in metered dose inhalers which accomplish the same end.
The patient's inhalation then carries the medication aerosol into the air passages via a mouthpiece. Current powder inhaler systems require strong inhalation on the part of the patient. They have not worked effectively with patients who cannot inhale vigorously.
In the metered dose inhalers noted above, it is common practice to include surfactants such as oleic acid. This presents problems. The fluorocarbon-medication suspension emerges as a liquid jet from the end of the valve stem or from the end of a cannula attached to the valve stem through which the metered dose inhaler contents have been forced and about 80 percent of it is deposited within three or four centimeters of the end of the valve or cannula. This results in an inefficient delivery system. It further has the disadvantage that large amounts of the surfactant material is deposited on the lining of the trachea, and the first few bronchi. It has been demonstrated that this causes injury to the airway lining with ulceration.
Over about the last 25 years systems for delivering medications to the lungs such as aerosol type delivery systems have become increasingly important for the treatment of airway diseases, particularly asthma and chronic obstructive pulmonary diseases, such as chronic bronchitis and emphysema as well as bronchiolitis and bronchiectasis. Other aerosol medications include mucolytic agents to thin secretions, the newest of which is deoxyribonuclease made by a recombinant method (rhDN-ase).
It is becoming increasingly important to deliver antibiotics directly to the airway for chronic illnesses such as cystic fibrosis, for treating a type of pneumonia in immunosuppressed patients (e.g., in AIDS), and for providing a new class of medications (sodium channel blockers) in cystic fibrosis to "lubricate" the secretions and make them easier to cough up or remove as a result of the action of cilia.
Aerosol systems for delivering medication directly to the patient's lungs generally fall into one of two categories, either (1) active or (2) passive. "Active" devices include (a) metered dose inhaler and (b) wet nebulizers. The pressurized canister metered dose inhaler generates the aerosol and directs it towards the patient independently of the patient's force of inhalation. This provides aerosol to the patient in a manner similar to so called "wet nebulizers" that aerosolize a drug solution. These "wet nebulizers" are jet nebulizers using the venturi principle, the energy source being compressed air which also serves to direct aerosol towards the spontaneously breathing or ventilation assisted patient, and ultrasonic nebulizers utilizing high speed vibration of a piezo-electric crystal and a blower fan to carry the medication aerosol to the patient. These are all active aerosol devices, since with the jet nebulizer it is the flow of oxygen or air through the device that creates the aerosol and drives it towards the patient who can then breathe in from a mouthpiece or mask. The ultrasonic nebulizer generates the aerosol into a space from which it can be inhaled by the patient breathing normally to inhale the mist with each inhalation, even if that inhalation is not vigorous. In addition, a blower can be incorporated which pushes the aerosol from the ultrasonic generator toward a mask or mouthpiece from which the patient inhales.
In contrast, currently available powder inhalers are "passive" devices in that the drug powder must reside in a small reservoir from which the patient can suck it by creating a relatively high inspiratory flow rate, usually over 30 liters per minute, and sometimes as high as 90-120 liters per minute if the optimum dose of medication is to be provided. This type of device has the advantage that aerosol is inhaled automatically when the patient inhales vigorously, but has certain disadvantages in that (a) there is considerable variability in dose depending upon how vigorously the patient inhales; (b) during severe episodes of asthma it may not be possible to create the high flow rates necessary to get a full dose of the drug which is particularly true of children under the age of 6; and (c) the greatest efficiency for aerosol inhalation is achieved at low inspiratory flow rates, 45 liters per minute and below, because at high flow rates small particles have greater inertia and therefore act like larger particles, thereby tending to be deposited in the back of the throat and around the larynx by impaction rather than being carried into the airways of the lungs where the medication must be deposited to be effective.
Another disadvantage of some widely prescribed current powder systems relates to exposure to the humidity of the environment of the drug reservoir where the fine particles are stored. Since many drug particles are very hygroscopic, repeated or continual exposure to humidity will greatly reduce the available dose due to swelling and clumping.
In view of the foregoing, what is needed is a relatively simple, yet highly effective dispensing apparatus which will effectively provide medication in a mist or vapor form to the lungs of a patient without requiring the patient to inhale vigorously.